Nitrofurans are synthetic broad-spectrum antibiotics used in animal, aquaculture and honey production. Nitrofurans are antibacterial, antiprotozoan and growth promoters. In animal studies the parent drugs and their metabolites showed carcinogenic and mutagenic characteristics. For that reason, nitrofuran use in the treatment of animals used for food production is prohibited. Despite such bans, residues continue to appear in the food supply. In particular, metabolites of nitrofurans can be tissue or protein bound resulting in residue remaining long after administration of the parent drug.
Common parent nitrofuran drugs, and their respective side chains (the R groups), include: furazolidone (side chain: 3-amino-2-oxazolidinone=AOZ), furaltadone (side chain: 3-amino-5-morpholinomethyl-2-oxazolidinone=AMOZ), nitrofurantoin (side chain: 1-aminohydantoin=AHD) and nitrofurazone (side chain: semicarbazide=SEM). The structures are as follows:

Nitrofurans are rapidly metabolized. The in situ half-life can be less than two hours. During metabolism, the nitrofuran parent may be reduced, such as by one or more nitroreductases. In one such scenario, the basic nitrofuranyl moiety (the common portion attached to the R group), is transformed into a different chemical group, while the R group (on the right hand side of the nitrofuran parent structure) remains intact.
Several methods for determining the use of a nitrofuran parent drug are via indirect metabolite detection. Such methods include liquid chromatography with ultra violet detection (LC-UV), liquid chromatography with mass spectrometer detection (LC-MS), liquid chromatography with tandem mass spectrometer detection (LC-MS/MS) and immunodiagnostics. The metabolite can be protein bound and, therefore, a hydrolysis step is used to cleave the side chain.
For UV detection, the released side chain can form a hydrazone derivative with 2-nitrobenzaldehyde. For example, in the cases of furazolidone and furaltadone, hydrazones with the acronyms of NPAOZ and NPAMOZ, respectively, are formed by the above process. It is the hydrazones—NPAOZ and NPAMOZ—not the actual metabolite, that are targeted for detection. Those hydrolysis and derivatization reactions require 16-24 hours prior to sample detection.